Discovery signals and network synchronization signals design in LTE

ABSTRACT

Base stations (such as small cells) may support active and dormant states. To facilitate state transitions, these cells may transmit discovery signals. The transmission design of both discovery signals and network synchronization signals from small cells should provide for regular periodicity, while supporting the benefit of transitioning between active and dormant states. Disclosed is a method, a computer program product, and an apparatus that determine a first reference signal for at least one of discovery or measurement, and a second reference signal for synchronization, where both the first reference signal and the second reference signal are based on a same type of reference signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application Ser.No. 61/932,685, entitled “DISCOVERY SIGNALS AND NETWORK SYNCHRONIZATIONSIGNALS DESIGN IN LTE” and filed on Jan. 28, 2014, which is expresslyincorporated by reference herein in its entirety.

BACKGROUND

Field

The present disclosure relates generally to communication systems, andmore particularly, to discovery signals and network synchronizationsignal design in LTE.

Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power). Examples of such multiple-access technologies includecode division multiple access (CDMA) systems, time division multipleaccess (TDMA) systems, frequency division multiple access (FDMA)systems, orthogonal frequency division multiple access (OFDMA) systems,single-carrier frequency division multiple access (SC-FDMA) systems, andtime division synchronous code division multiple access (TD-SCDMA)systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example of a telecommunicationstandard is Long Term Evolution (LTE). LTE is a set of enhancements tothe Universal Mobile Telecommunications System (UMTS) mobile standardpromulgated by Third Generation Partnership Project (3GPP). LTE isdesigned to better support mobile broadband Internet access by improvingspectral efficiency, lowering costs, improving services, making use ofnew spectrum, and better integrating with other open standards usingOFDMA on the downlink (DL), SC-FDMA on the uplink (UL), andmultiple-input multiple-output (MIMO) antenna technology. However, asthe demand for mobile broadband access continues to increase, thereexists a need for further improvements in LTE technology. Preferably,these improvements should be applicable to other multi-accesstechnologies and the telecommunication standards that employ thesetechnologies.

SUMMARY

Small cell densification (e.g., low power base stations), has potentialbenefits through a more optimal use of spectrum, but also poseschallenging design issues in mobile communications. These design issuesmay include mobility handling, interference handling, etc. Macro cellsmay or may not be deployed in the same geographical region as smallcells. Small cells may be of the same carrier frequency (co-channel) ora different carrier frequency from macro cells.

In order to better manage small cells, the small cells support activeand dormant states. For example, a small cell may be in an active state(e.g., ON state) when it serves a minimum number of UEs, may enter adormant state (e.g., OFF state) when not serving any UEs, or may handoffUEs and enter a dormant state when serving less than some minimumthreshold of UEs. A small cell in the dormant state may be reactivatedand enter the active state when UEs come within proximity of the smallcell. In order to facilitate active/dormant state transitions of smallcells, the small cells may transmit discovery signals. In one example, asmall cell may be configured to transmit discovery signals while in thedormant state. In another example, a small cell may be configured totransmit discovery signals while either in the dormant state or theactive state.

One of the issues with designing small cells is to provide a design forthe transmission of both discovery signals and network synchronizationsignals with sufficiently regular periodicity, while supporting activeand dormant states. In an aspect of the disclosure, a method, a computerprogram product, and an apparatus are provided. The apparatus may be anevolved Node B (eNB). The apparatus determines a first reference signalfor at least one of discovery or measurement, and a second referencesignal for synchronization, where both the first reference signal andthe second reference signal are based on a same type of referencesignal. For example, the same type of reference signal may be apositioning reference signal (PRS). The apparatus transmits the firstreference signal in one or more symbols of a first set of subframes andtransmits the second reference signal in one or more symbols of a secondset of subframes, where the first set of subframes and the second set ofsubframes differ at least by one subframe.

In an aspect of the disclosure, a method, a computer program product,and an apparatus are provided. The apparatus may be a user equipment(UE). The apparatus receives at least one of a first reference signalfor at least one of discovery or measurement or a second referencesignal for synchronization, at least one of the first or secondreference signals having a bandwidth configured by a base station (BS),and detects at least one cell based on at least one of the first orsecond reference signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a network architecture.

FIG. 2 is a diagram illustrating an example of an access network.

FIG. 3 is a diagram illustrating an example of a DL frame structure inLTE.

FIG. 4 is a diagram illustrating an example of an UL frame structure inLTE.

FIG. 5 is a diagram illustrating an example of a radio protocolarchitecture for the user and control planes.

FIG. 6 is a diagram illustrating an example of an evolved Node B anduser equipment in an access network.

FIG. 7 is a diagram illustrating an example small cell deploymentconfiguration.

FIG. 8 is a diagram illustrating an example small cell deploymentconfiguration.

FIG. 9 is a diagram illustrating an example small cell deploymentconfiguration.

FIG. 10 is a diagram illustrating an example small cell deploymentconfiguration.

FIG. 11 is a diagram illustrating transmissions of reference signals bysmall cells.

FIG. 12 is a diagram illustrating a subframe of a TDD type frame.

FIG. 13 is a diagram illustrating a subframe of a TDD type frame.

FIG. 14 is a diagram illustrating a subframe of a TDD type frame.

FIG. 15 is a flow chart of a method of wireless communication.

FIG. 16 is a flow chart of a method of wireless communication.

FIG. 17 is a flow chart of a method of wireless communication.

FIG. 18 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an exemplary apparatus.

FIG. 19 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 20 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an exemplary apparatus.

FIG. 21 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, modules, components,circuits, steps, processes, algorithms, etc. (collectively referred toas “elements”). These elements may be implemented using electronichardware, computer software, or any combination thereof. Whether suchelements are implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions, etc.,whether referred to as software, firmware, middleware, microcode,hardware description language, or otherwise.

Accordingly, in one or more exemplary embodiments, the functionsdescribed may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on or encoded as one or more instructions or code on acomputer-readable medium. Computer-readable media includes computerstorage media. Storage media may be any available media that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can comprise a random-access memory (RAM), aread-only memory (ROM), an electrically erasable programmable ROM(EEPROM), compact disk ROM (CD-ROM) or other optical disk storage,magnetic disk storage or other magnetic storage devices, or any othermedium that can be used to carry or store desired program code in theform of instructions or data structures and that can be accessed by acomputer. Combinations of the above should also be included within thescope of computer-readable media.

FIG. 1 is a diagram illustrating an LTE network architecture 100. TheLTE network architecture 100 may be referred to as an Evolved PacketSystem (EPS) 100. The EPS 100 may include one or more user equipment(UE) 102, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)104, an Evolved Packet Core (EPC) 110, and an Operator's InternetProtocol (IP) Services 122. The EPS can interconnect with other accessnetworks, but for simplicity those entities/interfaces are not shown. Asshown, the EPS provides packet-switched services, however, as thoseskilled in the art will readily appreciate, the various conceptspresented throughout this disclosure may be extended to networksproviding circuit-switched services.

The E-UTRAN includes the evolved Node B (eNB) 106 and other eNBs 108,and may include a Multicast Coordination Entity (MCE) 128. The eNB 106provides user and control planes protocol terminations toward the UE102. The eNB 106 may be connected to the other eNBs 108 via a backhaul(e.g., an X2 interface). The MCE 128 allocates time/frequency radioresources for evolved Multimedia Broadcast Multicast Service (MBMS)(eMBMS), and determines the radio configuration (e.g., a modulation andcoding scheme (MCS)) for the eMBMS. The MCE 128 may be a separate entityor part of the eNB 106. The eNB 106 may also be referred to as a basestation, a Node B, an access point, a base transceiver station, a radiobase station, a radio transceiver, a transceiver function, a basicservice set (BSS), an extended service set (ESS), or some other suitableterminology. The eNB 106 provides an access point to the EPC 110 for aUE 102. Examples of UEs 102 include a cellular phone, a smart phone, asession initiation protocol (SIP) phone, a laptop, a personal digitalassistant (PDA), a satellite radio, a global positioning system, amultimedia device, a video device, a digital audio player (e.g., MP3player), a camera, a game console, a tablet, or any other similarfunctioning device. The UE 102 may also be referred to by those skilledin the art as a mobile station, a subscriber station, a mobile unit, asubscriber unit, a wireless unit, a remote unit, a mobile device, awireless device, a wireless communications device, a remote device, amobile subscriber station, an access terminal, a mobile terminal, awireless terminal, a remote terminal, a handset, a user agent, a mobileclient, a client, or some other suitable terminology.

The eNB 106 is connected to the EPC 110. The EPC 110 may include aMobility Management Entity (MME) 112, a Home Subscriber Server (HSS)120, other MMEs 114, a Serving Gateway 116, a Multimedia BroadcastMulticast Service (MBMS) Gateway 124, a Broadcast Multicast ServiceCenter (BM-SC) 126, and a Packet Data Network (PDN) Gateway 118. The MME112 is the control node that processes the signaling between the UE 102and the EPC 110. Generally, the MME 112 provides bearer and connectionmanagement. All user IP packets are transferred through the ServingGateway 116, which itself is connected to the PDN Gateway 118. The PDNGateway 118 provides UE IP address allocation as well as otherfunctions. The PDN Gateway 118 and the BM-SC 126 are connected to the IPServices 122. The IP Services 122 may include the Internet, an intranet,an IP Multimedia Subsystem (IMS), a PS Streaming Service (PSS), and/orother IP services. The BM-SC 126 may provide functions for MBMS userservice provisioning and delivery. The BM-SC 126 may serve as an entrypoint for content provider MBMS transmission, may be used to authorizeand initiate MBMS Bearer Services within a PLMN, and may be used toschedule and deliver MBMS transmissions. The MBMS Gateway 124 may beused to distribute MBMS traffic to the eNBs (e.g., 106, 108) belongingto a Multicast Broadcast Single Frequency Network (MBSFN) areabroadcasting a particular service, and may be responsible for sessionmanagement (start/stop) and for collecting eMBMS related charginginformation.

FIG. 2 is a diagram illustrating an example of an access network 200 inan LTE network architecture. In this example, the access network 200 isdivided into a number of cellular regions (cells) 202. One or more lowerpower class eNBs 208 may have cellular regions 210 that overlap with oneor more of the cells 202. The lower power class eNB 208 may be a femtocell (e.g., home eNB (HeNB)), pico cell, micro cell, or remote radiohead (RRH). The macro eNBs 204 are each assigned to a respective cell202 and are configured to provide an access point to the EPC 110 for allthe UEs 206 in the cells 202. There is no centralized controller in thisexample of an access network 200, but a centralized controller may beused in alternative configurations. The eNBs 204 are responsible for allradio related functions including radio bearer control, admissioncontrol, mobility control, scheduling, security, and connectivity to theserving gateway 116. An eNB may support one or multiple (e.g., three)cells (also referred to as a sectors). The term “cell” can refer to thesmallest coverage area of an eNB and/or an eNB subsystem serving areparticular coverage area. Further, the terms “eNB,” “base station,” and“cell” may be used interchangeably herein.

The modulation and multiple access scheme employed by the access network200 may vary depending on the particular telecommunications standardbeing deployed. In LTE applications, OFDM is used on the DL and SC-FDMAis used on the UL to support both frequency division duplex (FDD) andtime division duplex (TDD). As those skilled in the art will readilyappreciate from the detailed description to follow, the various conceptspresented herein are well suited for LTE applications. However, theseconcepts may be readily extended to other telecommunication standardsemploying other modulation and multiple access techniques. By way ofexample, these concepts may be extended to Evolution-Data Optimized(EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interfacestandards promulgated by the 3rd Generation Partnership Project 2(3GPP2) as part of the CDMA2000 family of standards and employs CDMA toprovide broadband Internet access to mobile stations. These concepts mayalso be extended to Universal Terrestrial Radio Access (UTRA) employingWideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA;Global System for Mobile Communications (GSM) employing TDMA; andEvolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSMare described in documents from the 3GPP organization. CDMA2000 and UMBare described in documents from the 3GPP2 organization. The actualwireless communication standard and the multiple access technologyemployed will depend on the specific application and the overall designconstraints imposed on the system.

The eNBs 204 may have multiple antennas supporting MIMO technology. Theuse of MIMO technology enables the eNBs 204 to exploit the spatialdomain to support spatial multiplexing, beamforming, and transmitdiversity. Spatial multiplexing may be used to transmit differentstreams of data simultaneously on the same frequency. The data streamsmay be transmitted to a single UE 206 to increase the data rate or tomultiple UEs 206 to increase the overall system capacity. This isachieved by spatially precoding each data stream (i.e., applying ascaling of an amplitude and a phase) and then transmitting eachspatially precoded stream through multiple transmit antennas on the DL.The spatially precoded data streams arrive at the UE(s) 206 withdifferent spatial signatures, which enables each of the UE(s) 206 torecover the one or more data streams destined for that UE 206. On theUL, each UE 206 transmits a spatially precoded data stream, whichenables the eNB 204 to identify the source of each spatially precodeddata stream.

Spatial multiplexing is generally used when channel conditions are good.When channel conditions are less favorable, beamforming may be used tofocus the transmission energy in one or more directions. This may beachieved by spatially precoding the data for transmission throughmultiple antennas. To achieve good coverage at the edges of the cell, asingle stream beamforming transmission may be used in combination withtransmit diversity.

FIG. 3 is a diagram 300 illustrating an example of a DL frame structurein LTE. A frame (10 ms) may be divided into 10 equally sized subframes.Each subframe may include two consecutive time slots. A resource gridmay be used to represent two time slots, each time slot including aresource block. The resource grid is divided into multiple resourceelements. In LTE, for a normal cyclic prefix, a resource block contains12 consecutive subcarriers in the frequency domain and 7 consecutiveOFDM symbols in the time domain, for a total of 84 resource elements.For an extended cyclic prefix, a resource block contains 12 consecutivesubcarriers in the frequency domain and 6 consecutive OFDM symbols inthe time domain, for a total of 72 resource elements. Some of theresource elements, indicated as R 302, 304, include DL reference signals(DL-RS). The DL-RS include Cell-specific RS (CRS) (also sometimes calledcommon RS) 302 and UE-specific RS (UE-RS) 304. UE-RS 304 are transmittedonly on the resource blocks upon which the corresponding physical DLshared channel (PDSCH) is mapped. The number of bits carried by eachresource element depends on the modulation scheme. Thus, the moreresource blocks that a UE receives and the higher the modulation scheme,the higher the data rate for the UE.

FIG. 4 is a diagram 400 illustrating an example of an UL frame structurein LTE. The available resource blocks for the UL may be partitioned intoa data section and a control section. The control section may be formedat the two edges of the system bandwidth and may have a configurablesize. The resource blocks in the control section may be assigned to UEsfor transmission of control information. The data section may includeall resource blocks not included in the control section. The UL framestructure results in the data section including contiguous subcarriers,which may allow a single UE to be assigned all of the contiguoussubcarriers in the data section.

A UE may be assigned resource blocks 410 a, 410 b in the control sectionto transmit control information to an eNB. The UE may also be assignedresource blocks 420 a, 420 b in the data section to transmit data to theeNB. The UE may transmit control information in a physical UL controlchannel (PUCCH) on the assigned resource blocks in the control section.The UE may transmit only data or both data and control information in aphysical UL shared channel (PUSCH) on the assigned resource blocks inthe data section. A UL transmission may span both slots of a subframeand may hop across frequency.

FIG. 5 is a diagram 500 illustrating an example of a radio protocolarchitecture for the user and control planes in LTE. The radio protocolarchitecture for the UE and the eNB is shown with three layers: Layer 1,Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer andimplements various physical layer signal processing functions. The L1layer will be referred to herein as the physical layer 506. Layer 2 (L2layer) 508 is above the physical layer 506 and is responsible for thelink between the UE and eNB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control(MAC) sublayer 510, a radio link control (RLC) sublayer 512, and apacket data convergence protocol (PDCP) 514 sublayer, which areterminated at the eNB on the network side. Although not shown, the UEmay have several upper layers above the L2 layer 508 including a networklayer (e.g., IP layer) that is terminated at the PDN gateway 118 on thenetwork side, and an application layer that is terminated at the otherend of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 514 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between eNBs. The RLC sublayer 512 provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to hybrid automatic repeat request (HARQ). The MACsublayer 510 provides multiplexing between logical and transportchannels. The MAC sublayer 510 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNBis substantially the same for the physical layer 506 and the L2 layer508 with the exception that there is no header compression function forthe control plane. The control plane also includes a radio resourcecontrol (RRC) sublayer 516 in Layer 3 (L3 layer). The RRC sublayer 516is responsible for obtaining radio resources (e.g., radio bearers) andfor configuring the lower layers using RRC signaling between the eNB andthe UE.

FIG. 6 is a block diagram of an eNB 610 in communication with a UE 650in an access network. In the DL, upper layer packets from the corenetwork are provided to a controller/processor 675. Thecontroller/processor 675 implements the functionality of the L2 layer.In the DL, the controller/processor 675 provides header compression,ciphering, packet segmentation and reordering, multiplexing betweenlogical and transport channels, and radio resource allocations to the UE650 based on various priority metrics. The controller/processor 675 isalso responsible for HARQ operations, retransmission of lost packets,and signaling to the UE 650.

The transmit (TX) processor 616 implements various signal processingfunctions for the L1 layer (i.e., physical layer). The signal processingfunctions include coding and interleaving to facilitate forward errorcorrection (FEC) at the UE 650 and mapping to signal constellationsbased on various modulation schemes (e.g., binary phase-shift keying(BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying(M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded andmodulated symbols are then split into parallel streams. Each stream isthen mapped to an OFDM subcarrier, multiplexed with a reference signal(e.g., pilot) in the time and/or frequency domain, and then combinedtogether using an Inverse Fast Fourier Transform (IFFT) to produce aphysical channel carrying a time domain OFDM symbol stream. The OFDMstream is spatially precoded to produce multiple spatial streams.Channel estimates from a channel estimator 674 may be used to determinethe coding and modulation scheme, as well as for spatial processing. Thechannel estimate may be derived from a reference signal and/or channelcondition feedback transmitted by the UE 650. Each spatial stream maythen be provided to a different antenna 620 via a separate transmitter618TX. Each transmitter 618TX may modulate an RF carrier with arespective spatial stream for transmission.

At the UE 650, each receiver 654RX receives a signal through itsrespective antenna 652. Each receiver 654RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 656. The RX processor 656 implements various signalprocessing functions of the L1 layer. The RX processor 656 may performspatial processing on the information to recover any spatial streamsdestined for the UE 650. If multiple spatial streams are destined forthe UE 650, they may be combined by the RX processor 656 into a singleOFDM symbol stream. The RX processor 656 then converts the OFDM symbolstream from the time-domain to the frequency domain using a Fast FourierTransform (FFT). The frequency domain signal comprises a separate OFDMsymbol stream for each subcarrier of the OFDM signal. The symbols oneach subcarrier, and the reference signal, are recovered and demodulatedby determining the most likely signal constellation points transmittedby the eNB 610. These soft decisions may be based on channel estimatescomputed by the channel estimator 658. The soft decisions are thendecoded and deinterleaved to recover the data and control signals thatwere originally transmitted by the eNB 610 on the physical channel. Thedata and control signals are then provided to the controller/processor659.

The controller/processor 659 implements the L2 layer. Thecontroller/processor can be associated with a memory 660 that storesprogram codes and data. The memory 660 may be referred to as acomputer-readable medium. In the UL, the controller/processor 659provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the core network. The upper layerpackets are then provided to a data sink 662, which represents all theprotocol layers above the L2 layer. Various control signals may also beprovided to the data sink 662 for L3 processing. Thecontroller/processor 659 is also responsible for error detection usingan acknowledgement (ACK) and/or negative acknowledgement (NACK) protocolto support HARQ operations.

In the UL, a data source 667 is used to provide upper layer packets tothe controller/processor 659. The data source 667 represents allprotocol layers above the L2 layer. Similar to the functionalitydescribed in connection with the DL transmission by the eNB 610, thecontroller/processor 659 implements the L2 layer for the user plane andthe control plane by providing header compression, ciphering, packetsegmentation and reordering, and multiplexing between logical andtransport channels based on radio resource allocations by the eNB 610.The controller/processor 659 is also responsible for HARQ operations,retransmission of lost packets, and signaling to the eNB 610.

Channel estimates derived by a channel estimator 658 from a referencesignal or feedback transmitted by the eNB 610 may be used by the TXprocessor 668 to select the appropriate coding and modulation schemes,and to facilitate spatial processing. The spatial streams generated bythe TX processor 668 may be provided to different antenna 652 viaseparate transmitters 654TX. Each transmitter 654TX may modulate an RFcarrier with a respective spatial stream for transmission.

The UL transmission is processed at the eNB 610 in a manner similar tothat described in connection with the receiver function at the UE 650.Each receiver 618RX receives a signal through its respective antenna620. Each receiver 618RX recovers information modulated onto an RFcarrier and provides the information to a RX processor 670. The RXprocessor 670 may implement the L1 layer.

The controller/processor 675 implements the L2 layer. Thecontroller/processor 675 can be associated with a memory 676 that storesprogram codes and data. The memory 676 may be referred to as acomputer-readable medium. In the UL, the control/processor 675 providesdemultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the UE 650. Upper layer packets fromthe controller/processor 675 may be provided to the core network. Thecontroller/processor 675 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

In order to boost cellular communication performance in a cellularnetwork, a number of small cells (e.g., low power base stations) may bedeployed within a cell area served by a macro cell. Small celldensification (e.g., increasing the number of proximate small cellswithin an area) poses challenging design issues in mobilecommunications. Such design issues may include mobility handling,interference handling, etc. Macro cells may or may not be deployed inthe same geographical region as small cells. Small cells may be of thesame carrier frequency (co-channel) or a different carrier frequencyfrom macro cells.

In order to better manage small cells, small cells may support activeand dormant states. For example, a small cell may be in an active state(e.g., ON state) when it serves at least one UE (or a minimum number ofUEs) and may be in a dormant state (e.g., OFF state) when not servingany UEs (or a minimum number of UEs). A small cell in the dormant statemay be reactivated and enter the active state when there are UEs movingclose to the small cell. In order to facilitate active/dormant statetransitions, small cells may transmit discovery signals. In one example,a small cell may be configured to transmit discovery signals while inthe dormant state. In another example, a small cell may be configured totransmit discovery signals while either in the dormant state or theactive state. For example, the discovery signals may be used for coarsetime/frequency synchronization and/or measurement.

FIG. 7 is a diagram 700 illustrating an example small cell deploymentconfiguration. FIG. 7 shows an outdoor deployment of a macro cell 702and small cells 704, which may operate within the same geographicalarea. In an aspect, the small cells 704 may include cell 1 705, cell 2707, and cell 3 709. In FIG. 7, the small cells 704 are coupled to oneanother through backhaul links 708 and 710. Furthermore, the small cells704 are coupled to the macro cell 702 thorough backhaul link 706. In theconfiguration of FIG. 7, the macro cell 702 and small cells 704 share afrequency band (e.g., frequency band F1).

FIG. 8 is a diagram 800 illustrating an example small cell deploymentconfiguration. FIG. 8 shows an outdoor deployment of a macro cell 802and small cells 804, which may operate within the same geographicalarea. In an aspect, the small cells 804 may include cell 1 805, cell 2807, and cell 3 809. In FIG. 8, the small cells 804 are coupled to oneanother through backhaul links 808 and 810. Furthermore, the small cells804 are coupled to the macro cell 802 thorough backhaul link 806. In theconfiguration of FIG. 8, the macro cell 802 uses a first frequency band(e.g., frequency band F1) and the small cells 804 use a second frequencyband (e.g., frequency band F2) different from the first frequency band.

FIG. 9 is a diagram 900 illustrating an example small cell deploymentconfiguration. FIG. 9 shows a macro cell 902 that is deployed outdoorsand small cells 904 that are deployed indoors, but which may operatewithin the same geographical area. In an aspect, the small cells 904 mayinclude cell 1 905, cell 2 907, and cell 3 909. In FIG. 9, the smallcells 904 are coupled to one another through backhaul links 908 and 910.Furthermore, the small cells 904 are coupled to the macro cell 902thorough backhaul link 906. In the configuration of FIG. 9, the macrocell 902 uses a first frequency band (e.g., frequency band F1) and thesmall cells 904 use a second frequency band (e.g., frequency band F2)different from the first frequency band.

FIG. 10 is a diagram 1000 illustrating an example small cell deploymentconfiguration. FIG. 10 shows small cells 1002 that are deployed indoors.In an aspect, the small cells 1002 may include cell 1 1005, cell 2 1007,and cell 3 1009. In FIG. 10, the small cells 1002 are coupled to oneanother through backhaul links 1004 and 1006. In the configuration ofFIG. 10, the small cells 1002 use either a first frequency band (e.g.,frequency band F1) or a second frequency band (e.g., frequency band F2).In the configurations of FIGS. 7 through 10, the users may bedistributed both for outdoor and indoor deployments.

Small cells (also referred to as base stations (BSs)), femto cells, picocells, or microcells, typically achieve synchronization using GPS and/orbackhaul timing signaling. Alternatively, small cells may achievesynchronization by listening to over-the-air signals (also referred toas network listening) transmitted by other small cells. When usingnetwork listening to achieve synchronization, a small cell may acquiretiming/frequency information from reference signals transmitted by othersmall cells. Moreover, such a small cell may provide timing/frequencyinformation via transmission of reference signals to different smallcells. Each of the small cells performing network listening may beassociated with a synchronization status and a stratum level. Forexample, a first small cell transmitting reference signals may have astratum level of N and a second small cell performing network listeningusing the reference signals may have a stratum level N+1. For example, afirst small cell acquiring timing via GPS may have a stratum level 0(e.g., N=0), while a second small cell performing network listeningbased on reference signals transmitted by the first small cell may havea stratum level 1 (e.g., N+1=1).

A small cell may monitor the CRSs transmitted from other small cells inthe MBSFN region of MBSFN subframes, in special subframes, or viacoordinated silence durations. Coordination via backhaul and/ornetwork-wide configuration may be used to ensure proper operation.Information, such as stratum level and synchronization status, may beshared over the backhaul and/or indicated through the arrangement of hownetwork synchronization signals are transmitted.

Some networks may employ dynamic TDD subframe configurations, alsoreferred to as enhanced interference management for traffic adaptation(eIMTA). In one implementation, a system information block 1 (SIB1) maybe used to broadcast a particular TDD DL/UL configuration for legacy andnew UEs in a semi-static manner. In another implementation, a group or aUE-specific signal can be communicated to new UEs to indicate adifferent TDD DL/UL subframe configuration in a dynamic manner. Forexample, such indication may be as fast as 10.0 ms. For example, a ULsubframe signaled in SIB1 may be indicated as a DL subframe. In anotherexample, a special subframe in SIB1 may be indicated as a regular DLsubframe. In one example, the possible DL/UL subframe configurationsdynamically indicated for a UE are limited to pre-configured orstandardized DL/UL subframe configurations.

FIG. 11 is a diagram 1100 illustrating transmissions of referencesignals by small cells. FIG. 11, small cells 1, 2, and 3 may transmitreference signals by implementing a TDM scheme. In an aspect, the smallcells 1, 2, and 3 may correspond to the small cells in the variousdeployments discussed supra with respect to FIGS. 7-10. For example,small cells 1, 2, and 3 in FIG. 11 may respectively correspond to cell 1705, cell 2 707, and cell 3 709 in FIG. 7. As further shown in FIG. 11,each small cell (e.g., cell 1) may transmit a reference signal indicatedby a solid line (e.g., reference signal 1102) that serves as a discoverysignal and a reference signal indicated by a patterned line (e.g.,reference signal 1108) that serves as a network synchronization signal.For example, the reference signals in FIG. 11 may be positioningreference signals (PRSs), CRSs, primary synchronization signals (PSSs),or secondary synchronization signals (SSSs).

In an aspect, the transmission of reference signals that serve asdiscovery signals may be configured differently from the transmission ofreference signals that serve as network synchronization signals. Forexample, reference signals that serve as discovery signals may betransmitted in a same set of subframes across different small cells.With reference to FIG. 11, for example, cells 1, 2, and 3 may transmitrespective reference signals 1102, 1104, and 1106 that serve asdiscovery signals within the same subframe at time t₀. However,reference signals that serve as network synchronization signals (e.g.,for network listening) may be transmitted in different subframes fordifferent stratum levels. For example, with reference to FIG. 11, cell 1at stratum level 0 may transmit reference signal 1108 at time t₁, cell 2at stratum level 1 may transmit reference signal 1110 at time t₂, andcell 3 at stratum level 2 may transmit reference signal 1112 at time t₃,where t₁<t₂<t₃. In an aspect, and as shown in FIG. 11, the referencesignals that serve as network synchronization signals may be transmittedwith less periodicity than reference signals that serve as discoverysignals.

In an aspect, one or more reference signals that serve as networksynchronization signals may be transmitted in the same subframe as areference signal that serves as a discovery signal. In such aspect, thereference signals that serve as discovery signals and the referencesignals that serve as network synchronization signals may be separate ordifferent when transmitted in a same subframe.

In an aspect, during a subframe when a small cell (e.g., cell 1) istransmitting a reference signal (e.g., reference signal 1108) thatserves as a network synchronization signal, other small cells (e.g.,cells 2 and 3) may remain silent (e.g., refrain from transmitting)during that sub frame to facilitate network synchronization for theother small cells. For example, as shown in FIG. 11, when cell 1transmits reference signal 1108 at time t₁, cells 2 and 3 remain silentat time t₁ to avoid interference with the reference signal 1108.Accordingly, when cell 2 transmits reference signal 1110 at time t₂,cell 3 remains silent at time t₂ to avoid interference with thereference signal 1110.

In an aspect, reference signals that serve as discovery signals andreference signals that serve as network synchronization signals may betransmitted in a same set of subframes at least for some stratum levels.In such aspect, reference signals that serve as network synchronizationsignals may be transmitted with less periodicity (at least from amonitoring perspective) than reference signals that serve as discoverysignals. In an aspect, the reference signals that serve as networksynchronization signals may be the same as the reference signals thatserve as discovery signals. In another aspect, the reference signalsthat serve as network synchronization signals may be different from thereference signals that serve as discovery signals.

In an aspect, reference signals that serve as discovery signals may bebased on a CRS and/or a PRS. For example, a small cell may transmit botha CRS and a PRS in a discovery subframe. A small cell may also transmita PSS and/or SSS in the discovery subframe for cell identification. Inan aspect, a CRS may be omitted in an MBSFN region of an MBSFN subframe.In an aspect, the presence of the PSS and/or SSS may depend on subframeindices and system frame structure (e.g., FDD or TDD). For example, whena small cell implements an FDD frame structure, a PSS and/or SSS may bepresent in subframes 0 and 5 and may not be present in subframes 1-4 and6-9 of an FDD frame. In such example, a CRS and/or PRS may be used forcell identification when the PSS and/or SSS are not present.Alternatively, in order to facilitate cell identification, the PSSand/or SSS may be present in all subframes containing the discoverysignals and/or network synchronization signals.

In an aspect, a UE may perform a measurement using a PRS, a CRS, or acombination of the PRS and CRS. In an aspect, a small cell may configurethe bandwidth of the PRS such that the PRS does not always occupy theentire downlink system bandwidth. For example, a small cell may apply adefault bandwidth for the PRS that includes the center 6 RBs. In anaspect, the energy per resource element (EPRE) of the PRS may beindicated to the UE or assumed by the UE so that the UE may perform ameasurement using a combination of the CRS and PRS. For example,regardless of the bandwidth of the PRS, the UE may assume that the EPREof the PRS is the same as the EPRE of the CRS.

In an aspect, reference signals that serve as network synchronizationsignals may be based on the CRS and/or PRS. In an aspect, a small cellmay transmit both the CRS and PRS in a network synchronization subframe.In such aspect, the small cell may also transmit a PSS and/or SSS forcell identification. In another aspect, the small cell may not transmitthe PSS and/or SSS. In an aspect, the small cell may omit the CRS in theMBSFN region of the MBSFN subframe. In an aspect, a UE may perform ameasurement using a PRS, a CRS, or a combination of the PRS and CRS. Forexample, the UE may use the PRS for cell identification when the CRS andthe PSS and/or SSS are not present in a network listening subframe. Inan aspect, a small cell may configure the bandwidth of the PRS such thatthe PRS does not always occupy the entire downlink system bandwidth. Forexample, a small cell may apply a default bandwidth for the PRS thatincludes the center 6 RBs.

In an aspect, when a small cell is using a TDD frame structure andapplies TDD DL/UL subframe configuration 0 (indicated in SIB1), MBSFNsubframes may not be configured for network listening. In an aspect, asmall cell may implement guard periods in special subframes for networklistening. In an aspect, a small cell may transmit the PRS in specialsubframes. In such aspect, the transmission of the PRS in guard periodsof these special subframes may be a simple truncated version of the PRSin regular subframes.

FIG. 12 is a diagram illustrating a subframe 1200 of a TDD type frame.As shown in FIG. 12, the subframe 1200 includes 14 symbols, such assymbols 1202, 1204, 1206, 1208, 1210, 1212, 1214, 1216, 1218, 1220,1222, 1224, 1226, and 1228 (e.g., symbols 0-13). In other aspects, thesubframe 1200 may include a greater or lesser number of symbols. In anaspect, the subframe 1200 may be a UL subframe allocated for ULtransmissions by a UE. In such aspect, a small cell may use the subframe1200 for transmitting reference signals that serve as networksynchronization signals. The same cell may ensure, via scheduling orsignaling, that no UL transmissions are performed in the subframe. As anexample, a small cell may identify the subframe 1200 in a broadcastmessage or a unicast message to one or more UEs. For example, a smallcell may identify the subframe 1200 in a SIB1 broadcast and UEs thatreceive the SIB1 broadcast may refrain from transmitting in the subframe1200. As an example, a small cell may identify the subframe 1200 in adedicated message and UEs that receive the dedicated message may refrainfrom transmitting in the subframe 1200.

In an aspect, the subframe 1200 allocated as a UL subframe may be usedas an MBSFN subframe, a regular DL subframe, or a subframe in which noCRS is transmitted. Accordingly, a small cell may transmit referencesignals that serve as network synchronization signals in the subframe1200. In an aspect, the reference signal may be a PRS, a CRS, a PSS, oran SSS. For example, as shown in FIG. 12, a small cell may transmit PRSsin symbols 1208, 1212, 1214, 1218, 1220, 1222, and 1226 (e.g., symbols3, 5, 6, 8-10, and 12) of the subframe 1200 and may not transmit in theempty symbols 1204, 1206, 1210, 1216, and 1224 (e.g., empty symbols 1,2, 4, 7, and 11), where the PRSs enable other small cells to synchronizewith the small cell. In an aspect, a small cell performing networklistening in the subframe may not transmit during the subframe 1200. Inanother aspect, a small cell performing network listening in thesubframe 1200 may be configured to transmit control information in oneor more symbols.

In an aspect, as shown in FIG. 12, a small cell may be configured not totransmit in the first symbol(s) (e.g., symbol 0 in case the small celldoes not have legacy control symbols, or symbol 2 in case the small cellhas two legacy control symbols in symbol 0 and symbol 1) and/or the lastsymbol(s) (e.g., symbol 13) in order to facilitate switching by thesmall cell from UL mode to DL mode (e.g., receive mode to transmit mode)and/or DL mode to UL mode (e.g., transmit mode to receive mode). In anaspect, UEs may be prohibited from transmitting during the subframe1200. In an aspect, UE transmissions may be managed by a small cell in atransparent manner.

FIG. 13 is a diagram illustrating a subframe 1300 of a TDD type frame.As shown in FIG. 13, the subframe 1300 includes 14 symbols, such assymbols 1302, 1304, 1306, 1308, 1310, 1312, 1314, 1316, 1318, 1320,1322, 1324, 1326, and 1328 (e.g., symbols 0-13). In other aspects, thesubframe 1300 may include a greater or lesser number of symbols. In anaspect, the subframe 1300 may be a UL subframe allocated for ULtransmissions by a UE. In such aspect, a small cell may use the subframe1300 for transmitting reference signals that serve as networksynchronization signals. The same cell may ensure, via scheduling orsignaling, that no UL transmissions are performed in the subframe. As anexample, a small cell may identify the subframe 1300 in a message to oneor more UEs. For example, a small cell may identify the subframe 1300 toUEs in a broadcast/groupcast message or a dedicated message and the UEsmay refrain from transmitting in the subframe 1300.

In an aspect, the subframe 1300 allocated as a UL subframe may be usedas an MBSFN subframe, a regular DL subframe, or a subframe in which noCRS is transmitted. Accordingly, a small cell may transmit referencesignals that serve as network synchronization signals in the subframe1300. In an aspect, the reference signal may be a PRS, a CRS, a PSS, oran SSS. For example, as shown in FIG. 13, a small cell may transmit PRSsin symbols 1304, 1306, 1308, 1312, 1314, 1318, 1320, 1322, and 1326(e.g., symbols 1-3, 5, 6, 8-10, and 12) of the subframe 1300 and may nottransmit in the empty symbols 1310, 1316, and 1324 (e.g., empty symbols4, 7, and 11), where the PRSs enable other small cells to synchronizewith the small cell. In an aspect, a small cell performing networklistening in the subframe may not to transmit during the subframe 1300.In another aspect, a small cell performing network listening in thesubframe 1300 may be configured to transmit control information in oneor more symbols.

In an aspect, as shown in FIG. 13, the small cell may be configured notto transmit in the first symbol(s) (e.g., symbol 0) and/or the lastsymbol(s) (e.g., symbol 13) in order to facilitate switching by thesmall cell from UL mode to DL mode and/or DL mode to UL mode. In anaspect, UEs may be prohibited from transmitting during the subframe1300. In an aspect, UE transmissions may be managed by a small cell in atransparent manner.

FIG. 14 is a diagram illustrating a subframe 1400 of a TDD type frame.As shown in FIG. 14, the subframe 1400 includes 14 symbols, such assymbols 1402, 1404, 1406, 1408, 1410, 1412, 1414, 1416, 1418, 1420,1422, 1424, 1426, and 1428 (e.g., symbols 0-13). In other aspects, thesubframe 1400 may include a greater or lesser number of symbols. In anaspect, the subframe 1400 may be a DL subframe allocated for DLtransmissions by a small cell. In such aspect, a small cell may use thesubframe 1400 for transmitting and/or receiving reference signals thatserve as network synchronization signals.

In an aspect, with reference to FIG. 14, a small cell performing networklistening may transmit reference signals in one or more symbols of thesubframe 1400 when the subframe 1400 is not an MBSFN subframe (e.g.,when CRS still needs to be transmitted). For example, the small cell maytransmit a CRS and control information in symbol 1402 (e.g., symbol 0)and CRSs in symbols 1410, 1416, and 1424 (e.g., symbols 4, 7, and 11).As shown in FIG. 14, the small cell may perform network listening byreceiving reference signals that serve as network synchronizationsignals in one or more symbols of the subframe 1400. For example, thesmall cell may receive a PRS in symbols 1406 and 1420 (e.g., symbols 2and 9) of subframe 1400. As further shown in FIG. 14, the subframe 1400may include reserved symbols to facilitate switching by the small cellfrom UL mode to DL mode and/or DL mode to UL mode. For example, aftertransmitting the CRS and control information in symbol 0, the small cellmay switch from the DL mode to the UL mode during symbol 1404 (e.g.,symbol 1) in order to receive the PRS in symbol 1406 (e.g., symbol 2).The small cell may then switch from the UL mode to the DL mode duringsymbol 1408 (e.g., symbol 3) in order to transmit the CRS in symbol 1410(e.g., symbol 4). In another aspect, when a small cell is not performingnetwork listening and is configured to transmit reference signals thatserve as network synchronization signals, the small cell may transmitsuch reference signals (e.g., PRS) in the subframe 1400 to enable othersmall cells to synchronize with the small cell.

In an aspect, a cyclic prefix (CP) for reference signals that serve asdiscovery signals and/or network synchronization signals is determined.The cyclic prefix may be at least one of a normal CP or an extended CP.If PRS is used as the reference signals that serve as discovery signalsand/or network synchronization signals, the CP for the reference signalsmay be determined in the same manner as the CP for a PRS used forpositioning purposes. Alternatively, the CP for the PRS that serves asdiscovery signals and/or network synchronization signals may beseparately determined compared with the CP for the PRS used forpositioning purposes. As an example, for a given small cell, the CP forthe PRS that serves as discovery signals and/or network synchronizationsignals may be determined as a normal CP, while the CP for the PRS usedfor positioning purposes may be determined as an extended CP.

In an aspect, each periodic transmission instance of discovery signalsand/or network synchronization signals may span L subframe(s), whereL≧1. As an example, network synchronization signals may be transmittedby a small cell every 640 ms, and within each transmission instance, thenetwork synchronization signals may be transmitted in two consecutivesubframes. The L subframes can be consecutive subframes. Examples ofconsecutive subframes may include consecutive downlink subframes (i.e.,excluding uplink subframes), or consecutive fixed downlink subframes(i.e., excluding uplink subframes, and downlink subframes subject todynamic change of subframe directions), or consecutive subframesincluding special subframes and/or uplink subframes. The L subframes canbe non-consecutive subframes as well. As an example, if L=2, the twosubframes can be subframes 0 and 5. The parameter L can bepre-determined or configurable. If the parameter L is configurable, theparameter L may be indicated to a UE or a neighboring small cell via abroadcast message or a dedicated message. The UE or the neighboringsmall cell may utilize these L consecutive subframes to improvediscovery related performance and/or network synchronization relatedperformance, e.g., via coherently or non-coherent combining.

In an aspect, a small cell may transmit parameters associated withreference signals that serve as discovery signals and/or networksynchronization signals to one or more UEs and/or one or more othernodes (such as eNBs). For example, the parameters may include theconfigured bandwidth for a reference signal, information identifying asubframe that includes the reference signal, a stratum level, and/or anenergy per resource element (EPRE) of a reference signal. In an aspect,a small cell may broadcast such parameters itself. In another aspect,the parameters may be broadcast to the one or more UEs from a differentsmall cell using the same or different carrier frequencies. In anotheraspect, a small cell may transmit the parameters to one or more UEs viadedicated signaling for RRC connected UEs. In another aspect, a smallcell may transmit the parameters to one or more UEs via backhaulsignaling.

FIG. 15 is a flow chart 1500 of a method of wireless communication. Themethod may be performed by an eNB. It should be understood that thesteps represented with dotted lines in FIG. 15 represent optional steps.As such, steps 1504, 1506, 1508, 1510, 1512, and 1518 represent optionalsteps in the wireless communication method 1500.

At step 1502, the eNB determines a first reference signal for at leastone of discovery or measurement, and a second reference signal forsynchronization. This may include scheduling the first and secondreference signals for transmission to one or more UEs. In an aspect,both the first reference signal and the second reference signal may bebased on a same type of reference signal, such as a PRS, a CRS, a PSS,or an SSS. For example, the first reference signal may allow a UE nearthe eNB to discover the eNB. For example, the second reference signalmay allow a second eNB to synchronize with the eNB.

At step 1504, the eNB determines a cyclic prefix for at least one of thefirst reference signal or the second reference signal, where thedetermined cyclic prefix is different from a cyclic prefix of the commonreference signal.

At step 1506, the eNB determines a downlink system bandwidth of the eNB.For example, the eNB may determine the downlink system bandwidth byidentifying a memory address of a memory device in which the downlinksystem bandwidth is stored and by executing an instruction to retrievethe downlink system bandwidth.

At step 1508, the eNB configures a bandwidth for the first referencesignal and/or the second reference signal. In an aspect, the configuredbandwidth may be equal to the downlink system bandwidth. In anotheraspect, the configured bandwidth is less than the downlink systembandwidth. For example, the eNB may configure the bandwidth by selectinga suitable bandwidth that is less than the downlink system bandwidth.

At step 1510, the eNB transmits an instruction to the UE to refrain fromtransmitting signals in the at least one subframe in the second set ofsubframes. This allows the small cell to use the subframe for networkand discovery signals, without uplink interference from the UE.

At step 1512, the eNB transmits one or more parameters associated withthe first reference signal and/or the second reference signal to anothernode. In an aspect, the node may be a UE or another eNB. In an aspect,the one or more parameters may include the configured bandwidth,information identifying a subframe (that includes at least one of thefirst reference signal or the second reference signal), a stratum level,and/or an EPRE of at least one of the first reference signal or thesecond reference signal.

At step 1514, the eNB transmits the first reference signal in one ormore symbols of a first set of subframes. In an aspect, the firstreference signal is transmitted using the configured bandwidth.

At step 1516, the eNB transmits the second reference signal in one ormore symbols of a second set of subframes. In an aspect, the secondreference signal is transmitted using the configured bandwidth. In anaspect, the first set of subframes and the second set of subframesdiffer at least by one subframe, such that the first set of subframesand second set of subframes are not identical. In an aspect, at leastone subframe in the second set of subframes is one of a special subframeor a UL subframe, wherein at least a portion of the at least onesubframe is allocated for transmission of UL signals by a UE. In anaspect, the first set of subframes and/or the second set of subframes isbased on a periodic configuration. In an aspect, the first referencesignal and/or the second reference signal is transmitted in two or moreconsecutive subframes.

Finally, at step 1518, the eNB refrains from transmitting during a firstsymbol and/or a second symbol in at least a subset of subframes in thesecond set of subframes. In an aspect, the first symbol precedes the oneor more symbols in which the second reference signal is transmitted andthe second symbol is subsequent to the one or more symbols in which thesecond reference signal is transmitted. In an aspect, the first symbolis a beginning symbol in a subframe and the second symbol is an endingsymbol in a subframe.

FIG. 16 is a flow chart 1600 of a method of wireless communication. Themethod may be performed by an eNB. It should be understood that thesteps represented with dotted lines in FIG. 16 represent optional steps.As such, step 1608 represents an optional step in the wirelesscommunication method 1600.

At step 1602, the eNB determines one or more symbols of a set ofsubframes in which at least one reference signal is to be received. Inan aspect, the at least one reference signal is for synchronization withat least a second eNB. In an aspect, each of the set of subframes is oneof a special subframe or a UL subframe, where at least a portion of thespecial subframe or the UL subframe is allocated for transmission of ULsignals by a UE. In an aspect, the at least one reference signal is aPRS.

At step 1604, the eNB refrains from transmitting during the determinedone or more symbols of the set of subframes.

At step 1606, the eNB receives the at least one reference signal in theone or more symbols of the set of subframes.

Finally, at step 1608, the eNB synchronizes with at least the secondbase station based on the received at least one reference signal.

FIG. 17 is a flow chart 1700 of a method of wireless communication. Themethod may be performed by a UE. It should be understood that the stepsrepresented with dotted lines in FIG. 17 represent optional steps. Assuch, step 1702 represents an optional step in the wirelesscommunication method 1700.

At step 1702, the UE receives one or more parameters associated with afirst reference signal and/or a second reference signal from the eNB. Inan aspect, the one or more parameters may include the configuredbandwidth, information identifying a subframe that includes at least oneof the first reference signal or the second reference signal, a stratumlevel, and/or an EPRE of at least one of the first reference signal orthe second reference signal.

At step 1704, the UE receives a first reference signal for at least oneof discovery or measurement and/or a second reference signal forsynchronization. In an aspect, the first and/or second reference signalshave a bandwidth configured by the eNB. In an aspect, the bandwidth isless than a downlink system bandwidth of the eNB. In an aspect, thefirst and/or second reference signals are based on a same type ofreference signal, such as a PRS, a CRS, a PSS, or an SSS.

Finally, at step 1706, the UE detects at least one cell (e.g., eNB)based on at least one of the first or second reference signals.

FIG. 18 is a conceptual data flow diagram 1800 illustrating the dataflow between different modules/means/components in an exemplaryapparatus 1802. The apparatus may be an eNB. The apparatus includes amodule 1804 that receives at least one reference signal 1805 in one ormore symbols of a set of subframes. The apparatus further includes amodule 1806 that determines a subframe in which the at least onereference signal 1805 is to be received. In an aspect, the module 1806may provide the determined subframe to the receiving module in signal1807. The apparatus further includes a module 1808 that receives the atleast one reference signal 1805 and synchronizes with at least a secondbase station 1850 based on the received at least one reference signal1805. For example, module 1808 may receive the at least one referencesignal 1805 in signal 1809 from the receiving module 1804. The apparatusfurther includes a module 1812 that determines a first reference signalfor at least one of discovery or measurement and a second referencesignal for synchronization, determines a cyclic prefix for at least oneof the first reference signal or the second reference signal, anddetermines a downlink system bandwidth of the eNB. The apparatus furtherincludes a module 1814 that configures a bandwidth for the firstreference signal and/or the second reference signal. In an aspect, themodule 1814 receives a signal 1815 indicating the determined downlinksystem bandwidth from the module 1812. The apparatus further includes amodule 1816 that receives the first and second reference signals viasignal 1819 from module 1812 and receives the determined bandwidth(s)1817 from the module 1814. The module 1816 transmits the first referencesignal 1818 in one or more symbols of a first set of subframes andtransmits the second reference signal 1821 in one or more symbols of asecond set of subframes. The module 1816 further transmits one or moreparameters 1820 associated with the first reference signal and/or thesecond reference signal to another node, and transmits an instruction1822 to the UE 1852 to refrain from transmitting signals in the at leastone subframe in the second set of subframes. The apparatus furtherincludes a module 1810 that refrains from transmitting during a firstsymbol and/or a second symbol in at least a subset of subframes in asecond set of subframes and refrains from transmitting during thedetermined one or more symbols of the set of subframes in which at leastone reference signal is to be received. In an aspect, the first symboland/or the second symbol in at least a subset of subframes in a secondset of subframes is received from the module 1812 in signal 1813. In anaspect, the subframe in which the at least one reference signal (e.g.,reference signal 1805) is to be received is indicated to the refrainingmodule 1810 in signal 1811.

The apparatus may include additional modules that perform each of thesteps of the algorithm in the aforementioned flow charts of FIGS. 15 and16. As such, each step in the aforementioned flow charts of FIGS. 15 and16 may be performed by a module and the apparatus may include one ormore of those modules. The modules may be one or more hardwarecomponents specifically configured to carry out the statedprocesses/algorithm, implemented by a processor configured to performthe stated processes/algorithm, stored within a computer-readable mediumfor implementation by a processor, or some combination thereof.

FIG. 19 is a diagram 1900 illustrating an example of a hardwareimplementation for an apparatus 1802′ employing a processing system1914. The processing system 1914 may be implemented with a busarchitecture, represented generally by the bus 1924. The bus 1924 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1914 and the overalldesign constraints. The bus 1924 links together various circuitsincluding one or more processors and/or hardware modules, represented bythe processor 1904, the modules 1804, 1806, 1808, 1810, 1812, 1814, and1816, and the computer-readable medium/memory 1906. The bus 1924 mayalso link various other circuits such as timing sources, peripherals,voltage regulators, and power management circuits, which are well knownin the art, and therefore, will not be described any further.

The processing system 1914 may be coupled to a transceiver 1910. Thetransceiver 1910 is coupled to one or more antennas 1920. Thetransceiver 1910 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1910 receives asignal from the one or more antennas 1920, extracts information from thereceived signal, and provides the extracted information to theprocessing system 1914, specifically the receiving module 1804. Inaddition, the transceiver 1910 receives information from the processingsystem 1914, specifically the transmission module 1816, and based on thereceived information, generates a signal to be applied to the one ormore antennas 1920. The processing system 1914 includes a processor 1904coupled to a computer-readable medium/memory 1906. The processor 1904 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 1906. The software, whenexecuted by the processor 1904, causes the processing system 1914 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 1906 may also be used forstoring data that is manipulated by the processor 1904 when executingsoftware. The processing system further includes at least one of themodules 1804, 1806, 1808, 1810, 1812, 1814, and 1816. The modules may besoftware modules running in the processor 1904, resident/stored in thecomputer readable medium/memory 1906, one or more hardware modulescoupled to the processor 1904, or some combination thereof. Theprocessing system 1914 may be a component of the eNB 610 and may includethe memory 676 and/or at least one of the TX processor 616, the RXprocessor 670, and the controller/processor 675.

In one configuration, the apparatus 1802/1802′ for wirelesscommunication includes means for determining a first reference signalfor at least one of discovery or measurement, and a second referencesignal for synchronization, means for transmitting the first referencesignal in one or more symbols of a first set of subframes, means fortransmitting the second reference signal in one or more symbols of asecond set of subframes, means for refraining from transmitting duringat least one of a first symbol or a second symbol in at least a subsetof subframes in the second set of subframes, where the first symbolprecedes the one or more symbols in which the second reference signal istransmitted and the second symbol is subsequent to the one or moresymbols in which the second reference signal is transmitted, means fortransmitting an instruction to a UE to refrain from transmitting signalsin the at least one subframe in the second set of subframes, means forconfiguring a bandwidth for at least one of the first reference signalor the second reference signal, means for determining a downlink systembandwidth of the first BS base station, wherein the configured bandwidthis less than the downlink system bandwidth, means for transmitting oneor more parameters associated with at least one of the first referencesignal or the second reference signal to another node, means fortransmitting at least one of a CRS, a PSS, and/or an SSS, means fordetermining a cyclic prefix for at least one of the first referencesignal or the second reference signal, where the determined cyclicprefix is different from a cyclic prefix of the common reference signal,means for determining a subframe in which at least one reference signalis to be received, means for refraining from transmitting during atleast one symbol of the subframe in which the at least one referencesignal is to be received, means for receiving the at least one referencesignal in the subframe, means for synchronizing with at least the secondbase station based on the received at least one reference signal. Theaforementioned means may be one or more of the aforementioned modules ofthe apparatus 1802 and/or the processing system 1914 of the apparatus1802′ configured to perform the functions recited by the aforementionedmeans. As described supra, the processing system 1914 may include the TXProcessor 616, the RX Processor 670, and the controller/processor 675.As such, in one configuration, the aforementioned means may be the TXProcessor 616, the RX Processor 670, and the controller/processor 675configured to perform the functions recited by the aforementioned means.

FIG. 20 is a conceptual data flow diagram 2000 illustrating the dataflow between different modules/means/components in an exemplaryapparatus 2002. The apparatus may be a UE. The apparatus includes amodule 2004 that receives one or more parameters (e.g., parameter(s)2012) associated with a first reference signal and/or a second referencesignal from an eNB (e.g., eNB 2050), and receives a first referencesignal (e.g., reference signal 2010) for at least one of discovery ormeasurement and/or a second reference signal (e.g., reference signal2011) for synchronization, where the first and/or second referencesignals have a bandwidth configured by the eNB. The apparatus furtherincludes a module 2006 that receives a signal 2005 indicating the atleast one of the first or second reference signals and detects at leastone cell (e.g., eNB 2050) based on at least one of the first or secondreference signals. The apparatus further includes a module 2008 thatreceives a signal 2007 indicating the detected at least one cell (e.g.,eNB 2050) and transmits UL signals (e.g., UL signal 2014) to the atleast one cell (e.g., eNB 2050).

The apparatus may include additional modules that perform each of thesteps of the algorithm in the aforementioned flow chart of FIG. 17. Assuch, each step in the aforementioned flow chart of FIG. 17 may beperformed by a module and the apparatus may include one or more of thosemodules. The modules may be one or more hardware components specificallyconfigured to carry out the stated processes/algorithm, implemented by aprocessor configured to perform the stated processes/algorithm, storedwithin a computer-readable medium for implementation by a processor, orsome combination thereof.

FIG. 21 is a diagram 2100 illustrating an example of a hardwareimplementation for an apparatus 2002′ employing a processing system2114. The processing system 2114 may be implemented with a busarchitecture, represented generally by the bus 2124. The bus 2124 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 2114 and the overalldesign constraints. The bus 2124 links together various circuitsincluding one or more processors and/or hardware modules, represented bythe processor 2104, the modules 2004, 2006, and 2008, and thecomputer-readable medium/memory 2106. The bus 2124 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 2114 may be coupled to a transceiver 2110. Thetransceiver 2110 is coupled to one or more antennas 2120. Thetransceiver 2110 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 2110 receives asignal from the one or more antennas 2120, extracts information from thereceived signal, and provides the extracted information to theprocessing system 2114, specifically the receiving module 2004. Inaddition, the transceiver 2110 receives information from the processingsystem 2114, specifically the transmission module 2008, and based on thereceived information, generates a signal to be applied to the one ormore antennas 2120. The processing system 2114 includes a processor 2104coupled to a computer-readable medium/memory 2106. The processor 2104 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 2106. The software, whenexecuted by the processor 2104, causes the processing system 2114 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 2106 may also be used forstoring data that is manipulated by the processor 2104 when executingsoftware. The processing system further includes at least one of themodules 2004, 2006, and 2008. The modules may be software modulesrunning in the processor 2104, resident/stored in the computer readablemedium/memory 2106, one or more hardware modules coupled to theprocessor 2104, or some combination thereof. The processing system 2114may be a component of the UE 650 and may include the memory 660 and/orat least one of the TX processor 668, the RX processor 656, and thecontroller/processor 659.

In one configuration, the apparatus 2002/2002′ for wirelesscommunication includes means for receiving at least one of a firstreference signal for at least one of discovery or measurement or asecond reference signal for synchronization, means for detecting atleast one cell based on at least one of the first or second referencesignals, means for receiving one or more parameters associated with atleast one of the first reference signal or the second reference signalfrom the BS, and means for transmitting UL signals.

The aforementioned means may be one or more of the aforementionedmodules of the apparatus 2002 and/or the processing system 2114 of theapparatus 2002′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 2114 mayinclude the TX Processor 668, the RX Processor 656, and thecontroller/processor 659. As such, in one configuration, theaforementioned means may be the TX Processor 668, the RX Processor 656,and the controller/processor 659 configured to perform the functionsrecited by the aforementioned means.

It is understood that the specific order or hierarchy of steps in theprocesses/flow charts disclosed is an illustration of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of steps in the processes/flow charts may berearranged. Further, some steps may be combined or omitted. Theaccompanying method claims present elements of the various steps in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects.” Unless specificallystated otherwise, the term “some” refers to one or more. Combinationssuch as “at least one of A, B, or C,” “at least one of A, B, and C,” and“A, B, C, or any combination thereof” include any combination of A, B,and/or C, and may include multiples of A, multiples of B, or multiplesof C. Specifically, combinations such as “at least one of A, B, or C,”“at least one of A, B, and C,” and “A, B, C, or any combination thereof”may be A only, B only, C only, A and B, A and C, B and C, or A and B andC, where any such combinations may contain one or more member or membersof A, B, or C. All structural and functional equivalents to the elementsof the various aspects described throughout this disclosure that areknown or later come to be known to those of ordinary skill in the artare expressly incorporated herein by reference and are intended to beencompassed by the claims. Moreover, nothing disclosed herein isintended to be dedicated to the public regardless of whether suchdisclosure is explicitly recited in the claims. No claim element is tobe construed as a means plus function unless the element is expresslyrecited using the phrase “means for.”

What is claimed is:
 1. A method of wireless communication for a firstbase station (BS) comprising: determining a first reference signal forat least one of discovery or measurement, and a second reference signalfor synchronization, wherein both the first reference signal and thesecond reference signal are based on a same type of reference signal;transmitting a first set of subframes including the first referencesignal in one or more symbols; and transmitting a second set ofsubframes including the second reference signal in one or more symbols,wherein the first set of subframes and the second set of subframesdiffer at least by one subframe and the first base station refrains fromtransmitting during at least one of a first symbol or a second symbol inat least a subset of subframes in the second set of subframes, the firstsymbol preceding the one or more symbols in which the second referencesignal is transmitted and the second symbol being subsequent to the oneor more symbols in which the second reference signal is transmitted,wherein the same type of reference signal is based on a Cell-SpecificReference Signal (CRS) or a Positioning Reference Signal (PRS) and has abandwidth configured by the first base station.
 2. The method of claim1, wherein the first symbol is a beginning symbol in a subframe and thesecond symbol is an ending symbol in a subframe.
 3. The method of claim1, wherein at least one subframe in the second set of subframes is oneof a special subframe or an uplink (UL) subframe, wherein at least aportion of the at least one subframe is allocated for transmission of ULsignals by a user equipment (UE).
 4. The method of claim 3, furthercomprising transmitting an instruction to a user equipment (UE) torefrain from transmitting signals in the at least one subframe in thesecond set of subframes.
 5. The method of claim 1, wherein the firstreference signal allows a user equipment (UE) near the first basestation to discover the first base station, and wherein the secondreference signal allows a second base station to synchronize with thefirst base station.
 6. The method of claim 1, further comprisingconfiguring a bandwidth for at least one of the first reference signalor the second reference signal, wherein at least one of the firstreference signal or the second reference signal is transmitted using theconfigured bandwidth.
 7. The method of claim 6, further comprisingdetermining a downlink system bandwidth of the first BS, wherein theconfigured bandwidth is less than the downlink system bandwidth.
 8. Themethod of claim 6, further comprising transmitting one or moreparameters associated with at least one of the first reference signal orthe second reference signal to another node, the one or more parameterscomprising at least one of the configured bandwidth, informationidentifying a subframe that includes at least one of the first referencesignal or the second reference signal, a stratum level, or an energy perresource element (EPRE) of at least one of the first reference signal orthe second reference signal.
 9. The method of claim 1, furthercomprising determining a cyclic prefix for at least one of the firstreference signal or the second reference signal, wherein the determinedcyclic prefix is different from a cyclic prefix of a common referencesignal.
 10. The method of claim 1, wherein at least one of the first setof subframes or the second set of subframes is based on a periodicconfiguration.
 11. The method of claim 10, wherein at least the firstreference signal or the second reference signal is transmitted in two ormore consecutive subframes.
 12. A first base station (BS) for wirelesscommunication, comprising: a memory; and at least one processor coupledto the memory and configured to: determine a first reference signal forat least one of discovery or measurement, and a second reference signalfor synchronization, wherein both the first reference signal and thesecond reference signal are based on a same type of reference signal;transmit a first set of subframes including the first reference signalin one or more symbols; and transmit a second set of subframes includingthe second reference signal in one or more symbols, wherein the firstset of subframes and the second set of subframes differ at least by onesubframe and the first base station refrains from transmitting during atleast one of a first symbol or a second symbol in at least a subset ofsubframes in the second set of subframes, the first symbol preceding theone or more symbols in which the second reference signal is transmittedand the second symbol being subsequent to the one or more symbols inwhich the second reference signal is transmitted, wherein at least oneof the first reference signal or the second reference signal is based ona Cell-Specific Reference Signal (CRS) or a Positioning Reference Signal(PRS) and has a bandwidth configured by the first base station.
 13. Thefirst BS of claim 12, wherein the first symbol is a beginning symbol ina subframe and the second symbol is an ending symbol in a subframe. 14.The first BS of claim 12, wherein at least one subframe in the secondset of subframes is one of a special subframe or an uplink (UL)subframe, wherein at least a portion of the at least one subframe isallocated for transmission of UL signals by a user equipment (UE). 15.The first BS of claim 14, wherein the at least one processor is furtherconfigured to transmit an instruction to a user equipment (UE) torefrain from transmitting signals in the at least one subframe in thesecond set of subframes.
 16. The first BS of claim 12, wherein the firstreference signal allows a user equipment (UE) near the first basestation to discover the first base station, and wherein the secondreference signal allows a second base station to synchronize with thefirst base station.
 17. The first BS of claim 12, wherein the same typeof reference signal is a positioning reference signal (PRS).
 18. Thefirst BS of claim 12, wherein the at least one processor is furtherconfigured to configure a bandwidth for at least one of the firstreference signal or the second reference signal, and wherein at leastone of the first reference signal or the second reference signal istransmitted using the configured bandwidth.
 19. The first BS of claim18, wherein the at least one processor is further configured todetermine a downlink system bandwidth of the first BS, wherein theconfigured bandwidth is less than the downlink system bandwidth.
 20. Thefirst BS of claim 18, wherein the at least one processor is furtherconfigured to transmit one or more parameters associated with at leastone of the first reference signal or the second reference signal toanother node, the one or more parameters comprising at least one of theconfigured bandwidth, information identifying a subframe that includesat least one of the first reference signal or the second referencesignal, a stratum level, or an energy per resource element (EPRE) of atleast one of the first reference signal or the second reference signal.21. The first BS of claim 12, wherein the at least one processor isfurther configured to determine a cyclic prefix for at least one of thefirst reference signal or the second reference signal, wherein thedetermined cyclic prefix is different from a cyclic prefix of a commonreference signal.
 22. The first BS of claim 12, wherein at least one ofthe first set of subframes or the second set of subframes is based on aperiodic configuration.
 23. The first BS of claim 22, wherein at leastthe first reference signal or the second reference signal is transmittedin two or more consecutive subframes.
 24. An apparatus for wirelesscommunication for a first base station (BS) comprising: means fordetermining a first reference signal for at least one of discovery ormeasurement, and a second reference signal for synchronization, whereinboth the first reference signal and the second reference signal arebased on a same type of reference signal; and means for transmitting afirst set of subframes including the first reference signal in one ormore symbols and transmitting a second set of subframes including thesecond reference signal in one or more symbols, where the first set ofsubframes and the second set of subframes differ at least by onesubframe, wherein the first base station refrains from transmittingduring at least one of a first symbol or a second symbol in at least asubset of subframes in the second set of subframes, the first symbolpreceding the one or more symbols in which the second reference signalis transmitted and the second symbol being subsequent to the one or moresymbols in which the second reference signal is transmitted, wherein thesame type of reference signal is based on a Cell-Specific ReferenceSignal (CRS) or a Positioning Reference Signal (PRS) and has a bandwidthconfigured by the first base station.
 25. The apparatus of claim 24,wherein the first symbol is a beginning symbol in a subframe and thesecond symbol is an ending symbol in a subframe.
 26. The apparatus ofclaim 24, wherein at least one subframe in the second set of subframesis one of a special subframe or an uplink (UL) subframe, wherein atleast a portion of the at least one subframe is allocated fortransmission of UL signals by a user equipment (UE).
 27. The apparatusof claim 26, further comprising means for transmitting an instruction toa user equipment (UE) to refrain from transmitting signals in the atleast one subframe in the second set of subframes.
 28. The apparatus ofclaim 24, wherein the first reference signal allows a user equipment(UE) near the first base station to discover the first base station, andwherein the second reference signal allows a second base station tosynchronize with the first base station.
 29. The apparatus of claim 24,further comprising means for configuring a bandwidth for at least one ofthe first reference signal or the second reference signal, wherein atleast one of the first reference signal or the second reference signalis transmitted using the configured bandwidth.
 30. The apparatus ofclaim 29, wherein the means for configuring determine a downlink systembandwidth of the first BS, wherein the configured bandwidth is less thanthe downlink system bandwidth.
 31. The apparatus of claim 29, whereinthe means for transmitting transmit one or more parameters associatedwith at least one of the first reference signal or the second referencesignal to another node, the one or more parameters comprising at leastone of the configured bandwidth, information identifying a subframe thatincludes at least one of the first reference signal or the secondreference signal, a stratum level, or an energy per resource element(EPRE) of at least one of the first reference signal or the secondreference signal.
 32. The apparatus of claim 24, wherein the means fordetermining determine a cyclic prefix for at least one of the firstreference signal or the second reference signal, wherein the determinedcyclic prefix is different from a cyclic prefix of a common referencesignal.
 33. The apparatus of claim 24, wherein at least one of the firstset of subframes or the second set of subframes is based on a periodicconfiguration.
 34. The apparatus of claim 33, wherein at least the firstreference signal or the second reference signal is transmitted in two ormore consecutive subframes.
 35. A non-transitory computer-readablemedium storing computer executable code for wireless communication for afirst base station (BS), comprising code to: determine a first referencesignal for at least one of discovery or measurement, and a secondreference signal for synchronization, wherein both the first referencesignal and the second reference signal are based on a same type ofreference signal; transmit a first set of subframes including the firstreference signal in one or more symbols; and transmit a second set ofsubframes including the second reference signal in one or more symbols,where the first set of subframes and the second set of subframes differat least by one subframe, wherein the first base station refrains fromtransmitting during at least one of a first symbol or a second symbol inat least a subset of subframes in the second set of subframes, the firstsymbol preceding the one or more symbols in which the second referencesignal is transmitted and the second symbol being subsequent to the oneor more symbols in which the second reference signal is transmitted,wherein the same type of reference signal is based on a Cell-SpecificReference Signal (CRS) or a Positioning Reference Signal (PRS) and has abandwidth configured by the first base station.
 36. Thecomputer-readable medium of claim 35, wherein the first symbol is abeginning symbol in a subframe and the second symbol is an ending symbolin a subframe.
 37. The computer-readable medium of claim 35, wherein atleast one subframe in the second set of subframes is one of a specialsubframe or an uplink (UL) subframe, wherein at least a portion of theat least one subframe is allocated for transmission of UL signals by auser equipment (UE).
 38. The computer-readable medium of claim 37,further comprising code to: transmit an instruction to a user equipment(UE) to refrain from transmitting signals in the at least one subframein the second set of subframes.
 39. The computer-readable medium ofclaim 35, wherein the first reference signal allows a user equipment(UE) near the first base station to discover the first base station, andwherein the second reference signal allows a second base station tosynchronize with the first base station.
 40. The computer-readablemedium of claim 35, further comprising code to: configure a bandwidthfor at least one of the first reference signal or the second referencesignal, wherein at least one of the first reference signal or the secondreference signal is transmitted using the configured bandwidth.
 41. Thecomputer-readable medium of claim 40, further comprising code to:determine a downlink system bandwidth of the first BS, wherein theconfigured bandwidth is less than the downlink system bandwidth.
 42. Thecomputer-readable medium of claim 40, further comprising code to:transmit one or more parameters associated with at least one of thefirst reference signal or the second reference signal to another node,the one or more parameters comprising at least one of the configuredbandwidth, information identifying a subframe that includes at least oneof the first reference signal or the second reference signal, a stratumlevel, or an energy per resource element (EPRE) of at least one of thefirst reference signal or the second reference signal.
 43. Thecomputer-readable medium of claim 35, further comprising code to:determine a cyclic prefix for at least one of the first reference signalor the second reference signal, wherein the determined cyclic prefix isdifferent from a cyclic prefix of a common reference signal.
 44. Thecomputer-readable medium of claim 35, wherein at least one of the firstset of subframes or the second set of subframes is based on a periodicconfiguration.
 45. The computer-readable medium of claim 44, wherein atleast the first reference signal or the second reference signal istransmitted in two or more consecutive subframes.